Friday's hotly anticipated SpaceX market debut could prove a defining moment for capital markets — and serve as a "referendum" on Elon Musk's leadership.

A successful SpaceX debut would confirm Musk's talent for grabbing investors' attention.

SpaceX is preparing for a stock market debut that could become the largest initial public offering in history. The Elon Musk-led company is seeking to raise about $75 billion at a…